Alkylation of phenols



United States Patent 3,426,358 ALKYLATION 0F PHENOLS Hans L. Schlichting, Grand Island, and Anthony D. Barbopoulos and Walter H. Prahl, Buffalo, N.Y., assignors to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Filed Nov. 19, 1965, Ser- No. 508,821 U.S. Cl. 260--621 6 Claims Int. Cl. C07c 37/16 ABSTRACT OF THE DISCLOSURE Alkylated phenolic compounds are produced by passing in the vapor phase a mixture of a phenolic compound having at least one reactive position, an alkylating compound, and a small but effective amount of hydrogen halide over an alumina catalyst, .and recovering the alkylation product from the reaction mixture. The process is highly selective to the orthoposition.

This invention relates to the alkylation of phenol and substituted phenols. More particularly, the invention relates to a catalytic vapor phase alkylation of phenols.

It is known that phenols, such as phenol, cresol, xylenol, resorcinol, pyrogallol, hydroquinone, and the like, may be al kylated by a vapor phase condensation with alcohols, alkyl halides, dialkyl ethers, or olefins, at elevated temperatures, in the presence of alumina as a catalyst. As previously carried out, these alkylations have been subject to considerable by-product formation, low yields, formation of polyalkylated phenols, as well as non-selective substitution.

Selectively substituted phenols are commercially desirable for various applications. For instance, ortho-cresol is used as an intermediary in the production of plastics, antioxidants, and other useful compounds; metaand paracresol are useful intermediates for preparing dyes pharmaceuticals, antioxidants, and so forth; and 2,6-xylenol is used as a starting material for polyphenylene oxide plastics and bisxylenol plastics.

It is an object of the present invention to provide an improved process for the alkylation of phenols. Another object of this invention is to provide a process for the alkylation of phenols whereby improved selective positioning of the alkyl substituent in the phenolic molecule is achieved. Other objects of the invention will be apparent from the following detailed description.

-In accordance with the practice of the invention it has now been found that excellent yields of selectively alkylated phenols can be obtained when an alumina catalyst containing reaction zone is established to which an alkylating compound and a phenol or phenolic compound are continuously fed under reaction conditions, and fed simultaneously therewith is a small but effective amount of a hydrogen halide. The alkylation product, e.g., the selectively alkylated phenolic compound, is thereafter recovered from the reaction mixture.

From a further description of the invention, it will be readily apparent that the novel process offers numerous advantages. The presence of a minor proportion of a hydrogen halide, under reaction conditions, provides: (1) reactivity at lower temperature, thus reducing undesirable decomposition, improving the yield, and contributing to the longer usefulness of the catalyst; (2) improved direction to monosubstitution over multi-substitution, thus avoiding the formation of more highly substituted tar and residue forming compounds and thereby enhancing the yield of the lower substituted compounds; and (3) an improved selectivity of reaction to ortho-alkylated products of phenols.

Phenolic reactants which may be effectively utilized in the process of the invention are those having not more than 25 carbon atoms, preferably containing 6 to 12 carbon atoms, and also containing at least one reactive position, preferably ortho. Such compounds, for example, may be phenol, isomeric cresols, isomeric xylenols, phenols having substittued thereon one or more alkyl radicals or groups such as ethyl, propyl, isopropyl, butyl, amyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, decyl, and the like. Also included are fused ring phenols, such as naphthols and similar compounds, as well as polyhydric phenols exemplified by resorcinol, pyrogallol and hydroquinone.

The alkylating compounds of the present invention are selected from the group consisting of alkyl alcohols, alkyl halides, alkyl ethers, wherein alkyl is of 1 to 18 carbon atoms, and alkenes of 2 to 18 carbon atoms. It is more preferred to employ those alkyl compounds which have 1 to 10 carbon atoms and those alkenes which have 2 to 10 carbon atoms, and most preferred to employ those having 1 to 6 carbon atoms and 2 to 6 carbon atoms, respectively. Typical examples of these include methanol, ethanol, propanol, isopropyl alcohol, butanol, hexanol, cyclohexanol, heptanol, octanol, decanol, methyl chloride, ethyl chloride, propyl bromide, decyl chloride, dimethyl ether, diethyl ether, ethylene, propylene, butylene, 3,4-dimethyl-2-hexene, and the like.

The alumina catalysts especially useful in the practice of the invention comprise the aluminum oxides having extensive surface areas and great adsorptive capacities. Such alumina may be obtained from natural sources or may be prepared synthetically, as described, for instance, in Catalysis, vol. I, P. H. Emmett, 327 (1954).

The hydrogen halide employed is most conveniently anhydrous hydrogen chloride gas, but aqueous hydrochloric acid of any concentration to satisfy the required hydrogen chloride concentration in the reaction zone may be used as well. Other suitable hydrogen halides include anhydrous or aqueous hydrogen bromide.

The use of a diluent, such as added steam, may offer advantages in particular cases of highly reactive phenol and alkyl components to reduce and control the rate of reaction. In general, steam in excess of the amounts of water formed in the reaction is not required, although such an excess is considered as within the scope of the present invention.

The phenol reactant of the present invention may be utilized in molar proportions which are stoichiometrically equivalent to the amount of alkylating compound employed or may be utilized in molar proportions which are substantially in excess of the stoichiometric amount. The excess of phenol may be as much as five or more times the stoichiometric amount, preferably three times the stoichiometric amount. It is to be understood, the greater portion of the excess will be present as unreacted phenol in the reaction product and may be recycled to the reaction zone.

The hydrogen halide employed as the catalyst activator may be introduced to the reaction in molar proportions based on a molar proportion of alkylating agent and may Three reactors were each packed with 400 parts of range from 0.005 :1 to 1:1, preferably 0.01:1 to 0.05:1. activated alumina granules and placed in electrically Residence time of the reactants in the reaction zone heated and controlled salt-baths. A mixture of phenol and may be greater than about one minute, but preferably the methanol (molar proportions PhOH:MeOI-I=2.85 l) residence time is maintained between 5 seconds and was fed continuously at the same hourly rate (105 parts/ seconds. Suitable operating temperatures for the reaction 5 hour) through a preheater system into each reactor, over may range from 150 degrees centigrade to 350 degrees a period of more than 100 hours. centigrade, although it is preferred to maintain the tem- In Experiment 1, a slow stream of HCl gas (about 1.125 perature in the range of 250 degrees centigrade to 325 parts of gas per hour) was additionally fed to the reactor,

degrees centigrade. While the foregoing temperatures rep- 10 while the reaction temperature was kept at 300 degrees resent the preferred temperatures, generally they may centigrade. The effluent streams of all three reactors was vary depending upon the vaporization temperatures of collected as condensate and analyzed by gas chromatogthe reactants. Although the pressure of the recation is raphy. Table I gives the reactants, amounts, and reaction maintained at atmospheric pressure, it is within the scope conditions employed as well as giving the results obtained.

TABLE I Example 1 Example 2 Example 3 Total Feed:

Phenol 4,900 parts 9,400 parts 9,400 parts. Methanol 1,120 parts 1,120 parts 1,120 parts. H01 gas 56 parts.-. Temperature. 300 C 345 C 300 0. Feed Rate--- 106 parts/hou.r 105 parts/hour 105 parts/hour. Condensate:

Water 630 parts 630 parts 630 parts.

6,579 parts 6,580 parts..- 6,579 parts. 105 parts 109 parts 1,080 parts. 2,490 parts 864 parts. 110 parts 325 parts. 115 parts 540 parts. 370 parts 366 parts. 50 parts 100 parts 90 parts.

of this invention to employ subatmospheric and super- The reaction temperature of Example 2 was raised to atmospheric pressures depending upon the design of the 345 degrees centigrade to obtain a comparable amount reactor. of anisole in the effluent. Advantageously, these examples The process of the invention may be carried out in any demonstrate that in accordance with the process of the suitable catalytic reaction chamber packed with grains or invention (1) the same consumption of methanol was pellets of alumina catalyst, as such or in combination with effected at a lower temperature, that is, at 300 degrees carriers, equipped with heating and/or preheating syscentigrade in Example 1 as compared to the 345 degrees terns, and having a separating and recovery system, such centigrade required in Example 2; (2) the percentage of as distillation solumns or extraction columns, whereby undesired polysubstituted compounds, i.e., xylenols and high boilers, based on mono-substituted and polysubstirecovery of the reaction products and recycling of the tuted compound produced, was substantially reduced to unreacted reactants and/or intermediaries may be ac- 4O complished. 13.4 percent in Example 1 as compared to the 18.7 per- Advantageously, a vertical column packed with alucent produced in Example 2 which was conducted in the mina catalyst and adapted to receive the feed stream, for absence of hydrogen chloride; (3) a substantial selecinstance, at the top and discharge the effluent at the bottivity to ortho-substitution over metaand para-substitutom may be effectively employed. In some instances, it iS tion is clearly shown in Example 1, wherein 91.7 percent possible to employ a fluidized bed reactor, wherein the of mono-substituted products is o-cresol as compared to catalyst is in a fluidized form. Additionally, it is within 50.4 percent in Example 2 conducted in the absence of the scope of the invention to utilize other known and hydrogen chloride; and (4) yields of desirable products convenient methods. such as the cresols and xylenols was increased as shown The etfluent of the reaction zone is processed so as to by the reduction of the 3.26 percent yield of high boilers separate the alkylation products. Suitable methods for the in Example 2 to 1.62 percent yield of high boilers in Exseparation of said reaction product from the reaction mixample 1 which was conducted in the presence of hydroture include distillation, fractionation or extraction. gen halide.

It is also within the scope of this invention to process When a phenolic compound, an alcohol and a hydrogen the efiluent of the reaction zone so as to separate therehalide listed below is used in place of the phenol, methafrom the unreacted phenolic compound and the reaction 1101 and hydrogen chloride, respectively, of Example 1, products of lower degree of alkylation than desired and similar oitho-alkylation occurs, producing the correspondto recycle said compounds to the reaction zone to effect ing compounds. additional alkylation. Phenolic compound: o-Cresol, rrr-cresol, p-cresol, 2,5-

The following examples are presented to illustrate fur- 6O xylenol, 3,5-xylenol, catechol, resorcinol, hydroquinone.

ther the novelty and utility of the present invention but Alcohol: Ethanol, propanol, butanol, cyclohexanol, not with the intention of unduly limiting the same. Unhexanol, octanol, decanol, methyl chloride, decyl chloless otherwise indicated, all temperatures are in degrees ride, methyl ether, ethylene, propylene, isobutylene, 3,4- centigrade and all parts and percentages are by weight. dimethyl-Z-hexene. V

EXAMPLES Hydrogen halide: Hydrogen bromide. The advantageous effects of the presence of small EXAMPLES amounts of hydrogen chloride on the vapor phase con- Employing the procedures described in Examples 2-4, densation of phenol and methanol in the presence of aluthe etfects of the presence of small amounts of hydrogen mina catalyst to form o-cresol are demonstrated by the chloride on the vapor phase condensation reaction of following three experiments conducted under the hereino-cresol with methanol to form 2,6-xylenol were demonafter mentioned and listed conditions. Only one reaction strated by the following three experiments. The results mixture contained hydrogen chloride in accordance with are given in Table II. Experiment #4 illustrates the procthe present invention. The other two illustrate previously ess conditions in accordance with the present invention,

known reaction conditions and results. while Experiments #5 and #6 illustrate previously known reaction conditions and results. The effluent streams of all three reactors was collected as condensate and analyzed by gas chromatography.

was treated to recover the 2,6-xylenol as product.

Advantageously, 87 percent of the xylenols formed was 2,6-xylenol. The yield of 2,6-xylenol expressed as a per- TABLE II Example 4 Example 5 Example 6 Total Feed:

o-Oresol 10,800 parts 10,800 parts 10,800 parts. Methanol.

Condensate:

Water 630 parts 630 parts 630 parts. o-Cresol 7,580 parts 7,578 parts 7,581 parts. o-Methyl-amsole. 60 parts"- 1 220 parts 2,6-xylenol 2,560 parts 918 parts 2,3-xylenol 122 parts 182 parts 2,4-xylenol 480 parts 730 parts. 2,5;xylenol 120 parts- 306 parts. High Bollers 290 parts 410 parts 350 parts.

The reaction temperature of Example 5 was raised to 345 degrees centigrade to obtain a comparable amount of o-methyl-anisole in the effluent. Advantageously, Ex- 2 amples 4-6 demonstrate that in accordance with the process of the invention (1) the same consumption of methanol was obtained at a lower temperature, that is, at 300 degrees centigrade in Example 4 as compared to the 350 degrees centigrade required in Example 5; (2) the percentage of undesired polysubstituted compounds, i.e., high boilers, based on monosubstituted compounds, i.e., 2,6-, 2,3-, 2,4-, and 2,5-xylenols, and undesired polysubstituted compounds, was substantially reduced to 8.1 percent in Example 4 as compared to the 11.4 percent produced in Example 5 conducted in the absence of hydrogen chloride; (3) a substantial selectivity to ortho-substitution over metaand para-substitution is clearly shown by Example 4, wherein 78.0 percent of the monosubstituted product is 2,6xylenol, as compared to 46.0 percent in Example 5 conducted in the absence of hydrogen chloride; and (4) yields of desirable products, i.e., xylenols was increased as shown by the reduction of the 11.4 percent yield of high boilers in Example 5 to 8.1 percent yield of high boilers in Example 4 which was conducted in the presence of hydrogen halide.

If it is desired to introduce more than one alkyl substituent to the phenolic compound, it is possible to achieve this result by operating in several steps, that is, isolating the partially alkylated intermediate and using it as the starting material in a subsequent alkylation operation. However, the preferred method comprises a one step operation accomplished by the internal recycling of the intermediate as illustrated by the Example 7 describing the production of 2,6-xylenol directly from phenol.

EXAMPLE 7 This example was conducted employing the procedure of Examples 24. The feed to the reactor was modified to consist of 2820 parts of phenol, 1920 parts of methanol and 95 parts of hydrogen chloride gas. In addition, 6580 parts of phenol, 12,900 parts of o-cresol, 110 parts of anisole, 60 parts of methylanisole all recovered from the efliuent were recycled to the reaction zone. The reaction temperature was maintained at 300 degrees centigrade, and the feed rate was 105 parts per hour.

The portion of the effluent consisting of phenol, o-cresol, anisole and methylanisole was isolated and recycled, while the portion consisting of 2,6-xylenol and high boilers centage of all the substituted phenols formed is 74 percent.

From the foregoing description and examples, it is apparent that various modifications are possible within the scope of this invention and it is therefore not to be construed as limiting the invention except as defined by the appended claims.

What is claimed is:

1. The process for the production of alkylated phenolic compounds comprising passing in the vapor phase at a temperature between about degrees centigrade and about 350 degrees centigrade, a mixture of methanol, 21 small but effective amount of a hydrogen halide selected from the group consisting of hydrogen chloride and hydrogen bromide in molar proportions based on alkylating compounds ranging from 0.005:l to 1:1, and a stoichiometric excess of a phenolic compound selected from the group consisting of phenol and o-cresol, over an alumina catalyst, and recovering the alkylation product from the reaction mixture.

2. A process in accordance with claim 1 wherein the unreacted phenolic compound and the reaction products of lower degree of alkylation than desired are recycled over the alumina catalyst.

3. A process in accordance with claim 1 wherein the phenolic compound is phenol.

4. A process in accordance with claim 1 wherein the phenolic compound is o-cresol.

5. The process for the production of o-cresol comprising passing in the vapor phase at a temperature of between about 150 degrees cntigrade and about 350 degrees centigrade, a mixture of methanol, a small but eifective amount of hydrogen chloride in a molar proportion based on alkylating compound ranging from 0.005 :1 to 1:1, and a stoichiometric excess of phenol, over an alumina catalyst, and recovering o-cresol.

6. The process for the production of 2,6-xylenol comprising passing in the vapor phase at a temperature between about 150 degrees centigrade and about 350 degrees centigrade a mixture of methanol, a small but effective amount of hydrogen chloride in a molar proportion between about 0.005 :1 to 1:1, and a stoichiometric excess of phenol and o-cresol, over an alumina catalyst, and recovering 2,6-xylenol.

References Cited UNITED STATES PATENTS 2,430,190 11/1947 Schmerling et a1. 2,448,942 9/1948 Winkler et a1 260621 LEON ZITVER, Primary Examiner.

H. ROBERTS, Assistant Examiner.

US. Cl. X.R. 

